In a typical rclone copy to a bucket/container based remote, before
this change we were doing a list, followed by a HEAD of the bucket to
check it existed before doing the copy. The fact the list succeeded
means the bucket exists so mark it OK at that point.
Issue #1421
This removes the old system of part accounting and replaces it with a
system of popping off the accounting reader and wrapping up new ones
as necessary.
This makes it much easier to carry the context down the chain of
wrapped readers and get the limiting as near as possible to the
output. This makes the accounting more accurate and the bandwidth
limiting smoother.
Fixes#2029 and Fixes#1443
The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.
The new code layout is documented in CONTRIBUTING.
